1. Field of the Invention
The present disclosure relates generally to an ion focusing member and more particularly, to an ion focusing member adapted to be applied in a mass spectrometer for gathering analyte ions. The present disclosure further relates to a mass spectrometer using the ion focusing member.
2. Description of the Related Art
Recently, the mass spectrometer using electrospray ionization (hereinafter referred to as ‘ESI’) device has been widely used in the fields of identification of synthesized compounds, detection of environmental toxic substances, analysis of energy ingredients, development of drugs, biological metabolomics or pharmacometabolomics, analysis of natural products, food analysis, etc.
In general, a mass spectrometer includes an ionization device, a mass analyzer and a detector. FIG. 1 shows a schematic diagram of ionization mechanism of commercial ESI device 10. The conventional ESI device 10 includes a metal capillary 11 having an open end 111 that opens toward a sample inlet 21 of a mass analyzer 20. When the ESI device 10 is in use, an electric field, for example, a potential difference of 3,000 V to 5,000 V, is established between the open end 111 and the sample inlet 21 of the mass analyzer 20. Subsequently, a sample solution 30 contained in the metal capillary 11 is forced out of the metal capillary 11 for traveling toward the open end 111. The sample solution 30 forms a Taylor Cone T that is filled with electric charges when it passes through the open end 111 due to the electric field present between the open end 111 and the sample inlet 21 and the surface tension of the sample solution 30 at the open end 111. As the electric field force overcomes the surface tension of the sample solution 30 at the open end 111, liquid droplets 31 containing multivalent electric charges are formed, that is, a so-called electrospray phenomenon occurs. The solvent contained in the liquid droplets 31 vaporizes by a nebulization gas 40 to form analyte ions 33 which in turn travel into the mass analyzer 20 through the sample inlet 21, a mass spectrum is thus obtained.
As shown in FIG. 1, because the metal capillary 11 of the conventional ESI mechanism may create the plume-like analyte ions 33, that is, the analyte ions 33 may form a dispersion area much larger than a sectional area of the sample inlet 21 of the mass analyzer 20, at least 50% of the analyte ions 33 cannot flow into the mass analyzer 20. As a result, the mass spectrometer equipped with the conventional ESI device has the problems that the signal strength of analyte is significantly decreased and the detection limit cannot be lowered.
In order to improve the aforesaid problems, many methods for focusing ions to be transmitted into mass spectrometer by controlling electric field such as Field Asymmetric Ion Mobility Spectrometry (hereinafter referred to as ‘FAIMS’) have been developed. However, FAIMS has limited effect on ion-focusing under the influence of Maxwell's equation and has limited applicability due to its large volume and expensive price as well as it is not adapted to various mass spectrometers.